Compressor turbine motor trains are known in the art. In a typical compressor turbine motor train a compressor receives power from a motor and a turbine sharing a common shaft. The compressor power is supplied by the net output of the turbine and motor. The motor interfaces with the electric grid via a drive system. At the electrical interface, the drive exchanges both real and reactive power with the electrical grid. The voltage and frequency of the electrical grid are a function of the real and reactive power drawn by the drive. The motor can also act as a generator to transmit power to the electrical grid if the turbine capacity exceeds the compressor load.
In normal operation, a plant process controller provides a command to a compressor control system to maintain a certain discharge pressure by adjusting a speed reference to the turbine control. Speed regulation is accomplished by a turbine control system. When the turbine is firing, the fuel flow is adjusted to change turbine power and regulate speed. The drive system commands the motor to make up any torque difference that is not met by the turbine. When the turbine is not firing, the drive performs the speed regulation function with the speed command passed from the turbine control system. Typically, the turbine control system manages the coordination and commands the drive control system.
In current systems the load level is dependent upon compressor and turbine operation with no feedback or automatic control from the electric grid operating system or other means to aid stability of the electrical gird. The compressor turbine motor train system cannot rapidly respond to changes in the electrical grid that can be caused by electrical faults, load rejection, or sudden loss of power generation.
Accordingly what is needed is a control system for a compressor turbine motor train where the electrical interface to the electrical grid is adjusted under automatic control to aid operation of the electric power grid. Such a control system could be used to leverage any flexibility in real power balance between the turbine and compressor load to aid regulation of electrical grid frequency, and also to utilize any reactive control capability of the motor drive to aid regulation of electrical grid voltage.